A motor controller includes: a motor control part for driving and controlling a motor; an estimated temperature computing part for computing an estimated temperature of a winding of the motor; and a motor protecting part for protecting the motor from being burned when the estimated temperature becomes larger than a predetermined temperature. A temperature rise value of the estimated temperature is computed according to operating conditions of the motor at the time of passing electric current through the winding. This temperature rise value is added to an estimated temperature stored in the estimated temperature storing part to update the estimate temperature. To compute the temperature rise value, an optimum temperature rise value is computed by the use of a plurality of temperature-rise value computing expressions.